//! This module handles fuzzy-searching of functions, structs and other symbols
//! by name across the whole workspace and dependencies.
//!
//! It works by building an incrementally-updated text-search index of all
//! symbols. The backbone of the index is the **awesome** `fst` crate by
//! @BurntSushi.
//!
//! In a nutshell, you give a set of strings to `fst`, and it builds a
//! finite state machine describing this set of strings. The strings which
//! could fuzzy-match a pattern can also be described by a finite state machine.
//! What is freaking cool is that you can now traverse both state machines in
//! lock-step to enumerate the strings which are both in the input set and
//! fuzz-match the query. Or, more formally, given two languages described by
//! FSTs, one can build a product FST which describes the intersection of the
//! languages.
//!
//! `fst` does not support cheap updating of the index, but it supports unioning
//! of state machines. So, to account for changing source code, we build an FST
//! for each library (which is assumed to never change) and an FST for each Rust
//! file in the current workspace, and run a query against the union of all
//! those FSTs.

use std::{
    cmp::Ordering,
    fmt,
    hash::{Hash, Hasher},
    ops::ControlFlow,
};

use base_db::{RootQueryDb, SourceRootId};
use fst::{Automaton, Streamer, raw::IndexedValue};
use hir::{
    Crate, Module,
    db::HirDatabase,
    import_map::{AssocSearchMode, SearchMode},
    symbols::{FileSymbol, SymbolCollector},
};
use rayon::prelude::*;
use rustc_hash::FxHashSet;

use crate::RootDatabase;

#[derive(Debug, Clone)]
pub struct Query {
    query: String,
    lowercased: String,
    mode: SearchMode,
    assoc_mode: AssocSearchMode,
    case_sensitive: bool,
    only_types: bool,
    libs: bool,
    exclude_imports: bool,
}

impl Query {
    pub fn new(query: String) -> Query {
        let lowercased = query.to_lowercase();
        Query {
            query,
            lowercased,
            only_types: false,
            libs: false,
            mode: SearchMode::Fuzzy,
            assoc_mode: AssocSearchMode::Include,
            case_sensitive: false,
            exclude_imports: false,
        }
    }

    pub fn only_types(&mut self) {
        self.only_types = true;
    }

    pub fn libs(&mut self) {
        self.libs = true;
    }

    pub fn fuzzy(&mut self) {
        self.mode = SearchMode::Fuzzy;
    }

    pub fn exact(&mut self) {
        self.mode = SearchMode::Exact;
    }

    pub fn prefix(&mut self) {
        self.mode = SearchMode::Prefix;
    }

    /// Specifies whether we want to include associated items in the result.
    pub fn assoc_search_mode(&mut self, assoc_mode: AssocSearchMode) {
        self.assoc_mode = assoc_mode;
    }

    pub fn case_sensitive(&mut self) {
        self.case_sensitive = true;
    }

    pub fn exclude_imports(&mut self) {
        self.exclude_imports = true;
    }
}

/// The set of roots for crates.io libraries.
/// Files in libraries are assumed to never change.
#[salsa::input(singleton, debug)]
pub struct LibraryRoots {
    #[returns(ref)]
    pub roots: FxHashSet<SourceRootId>,
}

/// The set of "local" (that is, from the current workspace) roots.
/// Files in local roots are assumed to change frequently.
#[salsa::input(singleton, debug)]
pub struct LocalRoots {
    #[returns(ref)]
    pub roots: FxHashSet<SourceRootId>,
}

/// The symbol indices of modules that make up a given crate.
pub fn crate_symbols(db: &dyn HirDatabase, krate: Crate) -> Box<[&SymbolIndex]> {
    let _p = tracing::info_span!("crate_symbols").entered();
    krate.modules(db).into_iter().map(|module| SymbolIndex::module_symbols(db, module)).collect()
}

// Feature: Workspace Symbol
//
// Uses fuzzy-search to find types, modules and functions by name across your
// project and dependencies. This is **the** most useful feature, which improves code
// navigation tremendously. It mostly works on top of the built-in LSP
// functionality, however `#` and `*` symbols can be used to narrow down the
// search. Specifically,
//
// - `Foo` searches for `Foo` type in the current workspace
// - `foo#` searches for `foo` function in the current workspace
// - `Foo*` searches for `Foo` type among dependencies, including `stdlib`
// - `foo#*` searches for `foo` function among dependencies
//
// That is, `#` switches from "types" to all symbols, `*` switches from the current
// workspace to dependencies.
//
// Note that filtering does not currently work in VSCode due to the editor never
// sending the special symbols to the language server. Instead, you can configure
// the filtering via the `rust-analyzer.workspace.symbol.search.scope` and
// `rust-analyzer.workspace.symbol.search.kind` settings. Symbols prefixed
// with `__` are hidden from the search results unless configured otherwise.
//
// | Editor  | Shortcut |
// |---------|-----------|
// | VS Code | <kbd>Ctrl+T</kbd>
pub fn world_symbols(db: &RootDatabase, query: Query) -> Vec<FileSymbol> {
    let _p = tracing::info_span!("world_symbols", query = ?query.query).entered();

    let indices: Vec<_> = if query.libs {
        LibraryRoots::get(db)
            .roots(db)
            .par_iter()
            .for_each_with(db.clone(), |snap, &root| _ = SymbolIndex::library_symbols(snap, root));
        LibraryRoots::get(db)
            .roots(db)
            .iter()
            .map(|&root| SymbolIndex::library_symbols(db, root))
            .collect()
    } else {
        let mut crates = Vec::new();

        for &root in LocalRoots::get(db).roots(db).iter() {
            crates.extend(db.source_root_crates(root).iter().copied())
        }
        crates
            .par_iter()
            .for_each_with(db.clone(), |snap, &krate| _ = crate_symbols(snap, krate.into()));
        let indices: Vec<_> =
            crates.into_iter().map(|krate| crate_symbols(db, krate.into())).collect();
        indices.iter().flat_map(|indices| indices.iter().cloned()).collect()
    };

    let mut res = vec![];
    query.search::<()>(&indices, |f| {
        res.push(f.clone());
        ControlFlow::Continue(())
    });
    res
}

#[derive(Default)]
pub struct SymbolIndex {
    symbols: Box<[FileSymbol]>,
    map: fst::Map<Vec<u8>>,
}

impl SymbolIndex {
    /// The symbol index for a given source root within library_roots.
    pub fn library_symbols(db: &dyn HirDatabase, source_root_id: SourceRootId) -> &SymbolIndex {
        // FIXME:
        #[salsa::interned]
        struct InternedSourceRootId {
            id: SourceRootId,
        }
        #[salsa::tracked(returns(ref))]
        fn library_symbols(
            db: &dyn HirDatabase,
            source_root_id: InternedSourceRootId<'_>,
        ) -> SymbolIndex {
            let _p = tracing::info_span!("library_symbols").entered();

            // We call this without attaching because this runs in parallel, so we need to attach here.
            hir::attach_db(db, || {
                let mut symbol_collector = SymbolCollector::new(db, true);

                db.source_root_crates(source_root_id.id(db))
                    .iter()
                    .flat_map(|&krate| Crate::from(krate).modules(db))
                    // we specifically avoid calling other SymbolsDatabase queries here, even though they do the same thing,
                    // as the index for a library is not going to really ever change, and we do not want to store
                    // the module or crate indices for those in salsa unless we need to.
                    .for_each(|module| symbol_collector.collect(module));

                SymbolIndex::new(symbol_collector.finish())
            })
        }
        library_symbols(db, InternedSourceRootId::new(db, source_root_id))
    }

    /// The symbol index for a given module. These modules should only be in source roots that
    /// are inside local_roots.
    pub fn module_symbols(db: &dyn HirDatabase, module: Module) -> &SymbolIndex {
        // FIXME:
        #[salsa::interned]
        struct InternedModuleId {
            id: hir::ModuleId,
        }

        #[salsa::tracked(returns(ref))]
        fn module_symbols(db: &dyn HirDatabase, module: InternedModuleId<'_>) -> SymbolIndex {
            let _p = tracing::info_span!("module_symbols").entered();

            // We call this without attaching because this runs in parallel, so we need to attach here.
            hir::attach_db(db, || {
                let module: Module = module.id(db).into();
                SymbolIndex::new(SymbolCollector::new_module(
                    db,
                    module,
                    !module.krate(db).origin(db).is_local(),
                ))
            })
        }

        module_symbols(db, InternedModuleId::new(db, hir::ModuleId::from(module)))
    }
}

impl fmt::Debug for SymbolIndex {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("SymbolIndex").field("n_symbols", &self.symbols.len()).finish()
    }
}

impl PartialEq for SymbolIndex {
    fn eq(&self, other: &SymbolIndex) -> bool {
        self.symbols == other.symbols
    }
}

impl Eq for SymbolIndex {}

impl Hash for SymbolIndex {
    fn hash<H: Hasher>(&self, hasher: &mut H) {
        self.symbols.hash(hasher)
    }
}

impl SymbolIndex {
    fn new(mut symbols: Box<[FileSymbol]>) -> SymbolIndex {
        fn cmp(lhs: &FileSymbol, rhs: &FileSymbol) -> Ordering {
            let lhs_chars = lhs.name.as_str().chars().map(|c| c.to_ascii_lowercase());
            let rhs_chars = rhs.name.as_str().chars().map(|c| c.to_ascii_lowercase());
            lhs_chars.cmp(rhs_chars)
        }

        symbols.par_sort_by(cmp);

        let mut builder = fst::MapBuilder::memory();

        let mut last_batch_start = 0;

        for idx in 0..symbols.len() {
            if let Some(next_symbol) = symbols.get(idx + 1)
                && cmp(&symbols[last_batch_start], next_symbol) == Ordering::Equal
            {
                continue;
            }

            let start = last_batch_start;
            let end = idx + 1;
            last_batch_start = end;

            let key = symbols[start].name.as_str().to_ascii_lowercase();
            let value = SymbolIndex::range_to_map_value(start, end);

            builder.insert(key, value).unwrap();
        }

        let map = builder
            .into_inner()
            .and_then(|mut buf| {
                fst::Map::new({
                    buf.shrink_to_fit();
                    buf
                })
            })
            .unwrap();
        SymbolIndex { symbols, map }
    }

    pub fn len(&self) -> usize {
        self.symbols.len()
    }

    pub fn memory_size(&self) -> usize {
        self.map.as_fst().size() + self.symbols.len() * size_of::<FileSymbol>()
    }

    fn range_to_map_value(start: usize, end: usize) -> u64 {
        debug_assert![start <= (u32::MAX as usize)];
        debug_assert![end <= (u32::MAX as usize)];

        ((start as u64) << 32) | end as u64
    }

    fn map_value_to_range(value: u64) -> (usize, usize) {
        let end = value as u32 as usize;
        let start = (value >> 32) as usize;
        (start, end)
    }
}

impl Query {
    pub(crate) fn search<'sym, T>(
        self,
        indices: &'sym [&SymbolIndex],
        cb: impl FnMut(&'sym FileSymbol) -> ControlFlow<T>,
    ) -> Option<T> {
        let _p = tracing::info_span!("symbol_index::Query::search").entered();
        let mut op = fst::map::OpBuilder::new();
        match self.mode {
            SearchMode::Exact => {
                let automaton = fst::automaton::Str::new(&self.lowercased);

                for index in indices.iter() {
                    op = op.add(index.map.search(&automaton));
                }
                self.search_maps(indices, op.union(), cb)
            }
            SearchMode::Fuzzy => {
                let automaton = fst::automaton::Subsequence::new(&self.lowercased);

                for index in indices.iter() {
                    op = op.add(index.map.search(&automaton));
                }
                self.search_maps(indices, op.union(), cb)
            }
            SearchMode::Prefix => {
                let automaton = fst::automaton::Str::new(&self.lowercased).starts_with();

                for index in indices.iter() {
                    op = op.add(index.map.search(&automaton));
                }
                self.search_maps(indices, op.union(), cb)
            }
        }
    }

    fn search_maps<'sym, T>(
        &self,
        indices: &'sym [&SymbolIndex],
        mut stream: fst::map::Union<'_>,
        mut cb: impl FnMut(&'sym FileSymbol) -> ControlFlow<T>,
    ) -> Option<T> {
        let ignore_underscore_prefixed = !self.query.starts_with("__");
        while let Some((_, indexed_values)) = stream.next() {
            for &IndexedValue { index, value } in indexed_values {
                let symbol_index = &indices[index];
                let (start, end) = SymbolIndex::map_value_to_range(value);

                for symbol in &symbol_index.symbols[start..end] {
                    let non_type_for_type_only_query = self.only_types
                        && !matches!(
                            symbol.def,
                            hir::ModuleDef::Adt(..)
                                | hir::ModuleDef::TypeAlias(..)
                                | hir::ModuleDef::BuiltinType(..)
                                | hir::ModuleDef::Trait(..)
                        );
                    if non_type_for_type_only_query || !self.matches_assoc_mode(symbol.is_assoc) {
                        continue;
                    }
                    // Hide symbols that start with `__` unless the query starts with `__`
                    let symbol_name = symbol.name.as_str();
                    if ignore_underscore_prefixed && symbol_name.starts_with("__") {
                        continue;
                    }
                    if self.exclude_imports && symbol.is_import {
                        continue;
                    }
                    if self.mode.check(&self.query, self.case_sensitive, symbol_name)
                        && let Some(b) = cb(symbol).break_value()
                    {
                        return Some(b);
                    }
                }
            }
        }
        None
    }

    fn matches_assoc_mode(&self, is_trait_assoc_item: bool) -> bool {
        !matches!(
            (is_trait_assoc_item, self.assoc_mode),
            (true, AssocSearchMode::Exclude) | (false, AssocSearchMode::AssocItemsOnly)
        )
    }
}

#[cfg(test)]
mod tests {

    use expect_test::expect_file;
    use salsa::Setter;
    use test_fixture::{WORKSPACE, WithFixture};

    use super::*;

    #[test]
    fn test_symbol_index_collection() {
        let (db, _) = RootDatabase::with_many_files(
            r#"
//- /main.rs

macro_rules! macro_rules_macro {
    () => {}
};

macro_rules! define_struct {
    () => {
        struct StructFromMacro;
    }
};

define_struct!();

macro Macro { }

struct Struct;
enum Enum {
    A, B
}
union Union {}

impl Struct {
    fn impl_fn() {}
}

struct StructT<T>;

impl <T> StructT<T> {
    fn generic_impl_fn() {}
}

trait Trait {
    fn trait_fn(&self);
}

fn main() {
    struct StructInFn;
}

const CONST: u32 = 1;
static STATIC: &'static str = "2";
type Alias = Struct;

mod a_mod {
    struct StructInModA;
}

const _: () = {
    struct StructInUnnamedConst;

    ()
};

const CONST_WITH_INNER: () = {
    struct StructInNamedConst;

    ()
};

mod b_mod;


use define_struct as really_define_struct;
use Macro as ItemLikeMacro;
use Macro as Trait; // overlay namespaces
//- /b_mod.rs
struct StructInModB;
pub(self) use super::Macro as SuperItemLikeMacro;
pub(self) use crate::b_mod::StructInModB as ThisStruct;
pub(self) use crate::Trait as IsThisJustATrait;
"#,
        );

        let symbols: Vec<_> = Crate::from(db.test_crate())
            .modules(&db)
            .into_iter()
            .map(|module_id| {
                let mut symbols = SymbolCollector::new_module(&db, module_id, false);
                symbols.sort_by_key(|it| it.name.as_str().to_owned());
                (module_id, symbols)
            })
            .collect();

        expect_file!["./test_data/test_symbol_index_collection.txt"].assert_debug_eq(&symbols);
    }

    #[test]
    fn test_doc_alias() {
        let (db, _) = RootDatabase::with_single_file(
            r#"
#[doc(alias="s1")]
#[doc(alias="s2")]
#[doc(alias("mul1","mul2"))]
struct Struct;

#[doc(alias="s1")]
struct Duplicate;
        "#,
        );

        let symbols: Vec<_> = Crate::from(db.test_crate())
            .modules(&db)
            .into_iter()
            .map(|module_id| {
                let mut symbols = SymbolCollector::new_module(&db, module_id, false);
                symbols.sort_by_key(|it| it.name.as_str().to_owned());
                (module_id, symbols)
            })
            .collect();

        expect_file!["./test_data/test_doc_alias.txt"].assert_debug_eq(&symbols);
    }

    #[test]
    fn test_exclude_imports() {
        let (mut db, _) = RootDatabase::with_many_files(
            r#"
//- /lib.rs
mod foo;
pub use foo::Foo;

//- /foo.rs
pub struct Foo;
"#,
        );

        let mut local_roots = FxHashSet::default();
        local_roots.insert(WORKSPACE);
        LocalRoots::get(&db).set_roots(&mut db).to(local_roots);

        let mut query = Query::new("Foo".to_owned());
        let mut symbols = world_symbols(&db, query.clone());
        symbols.sort_by_key(|x| x.is_import);
        expect_file!["./test_data/test_symbols_with_imports.txt"].assert_debug_eq(&symbols);

        query.exclude_imports();
        let symbols = world_symbols(&db, query);
        expect_file!["./test_data/test_symbols_exclude_imports.txt"].assert_debug_eq(&symbols);
    }
}
